Thermal retention-device

ABSTRACT

A heat retention device is disclosed in the form of a heating pad which includes an electrically resistive coil contained within a volume. The coil terminates at an electric coupler which is external of the volume. A heat retention mass is contained within the volume in thermal conductivity with the resistive element.

I. CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.08/581,929 filed with the United States Patent and Trademark office onJan. 24, 1996 and issued as U.S. Pat. No. 5,932,129 on Aug. 3, 1999.U.S. application Ser. No. 08/581,929 is a continuation-in-partapplication of U.S. application Ser. No. 08/394,491 filed with theUnited States Patent and Trademark Office on Feb. 27, 1995 and is nowabandoned. U.S. patent application Ser. Nos. 08/581,929 and 08/394,491are incorporated herein by reference.

II. BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to thermal retention devices for storing thermalenergy and releasing the thermal energy over time. More particularly,this invention pertains to a thermal retention device which utilizes aphase change material as a medium for storing and releasing thermalenergy.

2. Description of the Prior Art

The prior art includes so-called phase change materials for storingthermal energy. A phase change material is a material which includes asubstance which changes phase (for example, from solid state to liquidstate or from a liquid state to a gaseous state) upon the application ofthermal energy to the material. The process of changing phase results inenergy (referred to as latent heat) being stored in the material. Whenthe phase change reverses, the latent heat is released.

Phase change materials can be provided with a wide variety of phasechange temperatures (i.e., the temperature at which the phase changematerial changes phase). An example of a phase change material isdescribed more fully in U.S. Pat. No. 5,211,949 which describes ahydrocarbon dispersed within a finely divided silica. The phase changematerial stays in a powder form above and below the melting point of thehydrocarbon. The hydrocarbon melting point can be selected to be any oneof a number of different temperatures. The phase change material resultsin an effective storing of thermal energy with energy being released atabout the melting point of the hydrocarbon.

Numerous devices containing phase change materials are known in theprior art. For example, seat cushions are formed which will include afoam pad impregnated with a phase change material. The seat cushion iscontained within an envelope of plastic such as vinyl or the like. Theentire cushion may be placed in a source of thermal energy (for example,a conventional microwave oven). Energy is applied to the phase changematerial and the cushion will retain an elevated temperature for asubstantial period of time (commonly one to four hours).

Other means, in addition to phase change materials, are known forstoring energy. For example, U.S. Pat. No. 5,300,105 to Owens dated Apr.5, 1994 teaches a foam pad vacuum sealed in a plastic envelope. Theenvelope also contains a liquid which is heated by application ofmicrowave energy. The '105 patent teaches several uses for the inventionincluding therapeutic pads, toys and cushions.

While prior art microwave thermal retention devices are acceptable formany uses, there are certain applications where such devices havelimitations. For example, the user of such a device must have access toa source of the energy. In the case of a microwave thermal retentiondevice, the user must have access to a microwave oven to supply thenecessary energy to cause the phase change material or other heatretention means to store the energy. For many users, access to amicrowave oven is not practical. Also, for many users, there may be asubstantial period of time between which the energy is applied and thedevice is to be used. An example of such an inconvenience is where athermal retention device is to be used as a cushion for either outdooractivity or for stadium use at sporting events and the like. In suchcases, there may be a substantial period of time between the applicationof energy to the device and the use of the device.

III. SUMMARY OF THE INVENTION

According to a preferred embodiment of the present invention, a thermalretention device is disclosed which includes an envelope for defining anenclosed volume. An electrically resistive element is disposed withinthe envelope and terminates at an electric coupler which is adapted forcoupling to an external source of electric power. A heat retentionmaterial is contained within the envelope in thermal conductivity withthe resistive element.

IV. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment of the presentinvention in the form of a heating pad incorporating the invention ofthe present invention and shown with an internal envelop removed from acloth cover;

FIG. 2 is a cross-sectional view of the assembled heating pad of FIG. 1;

FIG. 3 is an end view of a first end of the heating pad of FIG. 1 takenalong lines 3—3 of FIG. 1;

FIG. 4 is an opposite end view of the heating pad of FIG. 1;

FIG. 5 is a plan view of a resistive heating element of the heating padof FIG. 1 shown in plan view;

FIG. 6 is a schematic representation of the heating coil shown in FIG.5;

FIG. 7 is a plan view of an alternating current power cord forenergizing the pad of FIG. 1;

FIG. 8 is a plan view of a direct current power cord for energizing thepad of FIG. 1;

FIG. 9 is a side cross-sectional view shown in schematic of analternative embodiment of the present invention; and

FIG. 10 is a still further embodiment of the present invention shown inside cross-section schematic.

V. DESCRIPTION OF A PREFERRED EMBODIMENT

With initial reference to FIG. 1, a heating pad 10 is shownincorporating the teachings of the present invention. It will beappreciated while the present invention is disclosed with reference to aheating pad such as a cushion or the like, that the teachings of thepresent invention are readily adapted to a wide variety of products anduses. For example, the present invention can be used in clothing (e.g.,footwear, mittens, etc.), food warming devices (e.g., beveragecontainers, serving dishes, bread warmers, etc.), toys to be warmed ascomforters and therapeutic pads.

A. First Embodiment

The heating pad 10 is substantially rectangular in shape. The pad 10includes an outer cloth covering 12 which is open at its opposite ends14, 16. Contained within cloth covering 12 is a sealed vinyl or plasticenvelope 18. Envelope 18 is completely sealed to define an internalvolume. Contained within the volume is an electric resistive element(FIGS. 2, 5 and 6) in the form of a plurality of wire coils 22.

The resistive element 22 in a preferred embodiment includes a firstresistive coil 24 and a second resistive coil 26. The coils 24, 26terminate at a coupling 28 which includes three female connectors 31, 32and 33. Connector 31 and connector 33 are electrically connected toopposite ends of coil 24. Connector 32 and connector 33 are connected toopposite end of coil 26 as best shown schematically in FIG. 6. Each ofcoils 26, 24 are connected to connector 33 through a thermal switch 30which will be more fully described. Also, as will be described, coil 24is intended for use in an alternating current circuit and coil 26 isintended for use in a direct current circuit. A coupling 28 forterminating the coils 24, 26 is shown and described in U.S. Pat. No.2,980,881.

The coils 24, 26 are disposed sandwiched between two layers of open cellfoam material 34, 36 (FIG. 2). The foam material 34, 36 is alsocontained within the volume of envelope 18. The coupling 28 is exteriorto the envelope 18 passing through and sealed at the envelope 18 atlocation 19. Also contained within envelope 18 is a microwave receptiveheat retention mass 20. While the heat retention mass need not be aphase change material (as will be described with reference toalternative embodiments), in the embodiment of FIGS. 1-6, the thermalretention mass 20 is a phase change material.

In the specific embodiment shown, a preferred phase change material 20is sold under the name “Michemlube 270R” available through Mechelman,Inc., 9080 Shell Road, Cincinnati, Ohio, Order No. A56141. Such a phasechange material is selected to have a phase change temperature of about140° F. and is a parfain based emulsion.

With the coils 24, 26, foam 34, 36 and phase change material 20contained within envelope 18, the envelope 18 (which is flexibleplastic) has a vacuum applied to its interior and the peripheral edgesof the envelope 18 are completely sealed while the vacuum is applied.Commonly assigned U.S. Pat. No. 5,300,105 teaches sealing a phase changeliquid and a foam pad within a flexible plastic envelope.

With the envelope 18 and its contents constructed as thus described, theenvelope 18 is contained within the cloth cover 12. The ends 16, 14 ofcloth cover 12 are initially open. As best shown in FIG. 3, end 16 isstitched shut substantially along its length but is open at a corner16A. The opening of corner 16A is sized to freely pass coupling 28.Opposing surfaces of the edge 16 at opening end 16A are provided withhook-and-loop fasteners 40, 41 (such as well-known Velcro™ fasteners) topermit the end 16A to be closed as snugly as possible around the cordextending from coupling 28. The opposite end 14 is also provided withhook-and-loop fasteners 42, 44 to permit end 14 to be closed.

To energize the resistive elements 24, 26, power cords 50, 60 areprovided as shown in FIGS. 7 and 8. Power cord 50 is an alternatingcurrent power cord having a standard male plug end 51 which may beplugged in any conventional wall outlet and terminating at a coupling 52having male connectors 53, 54, 55 disposed to be received and mate withthe female connectors 31, 32, 33 of coupling 28. Only connectors 53, 55are connected to plug 51 (connector 54 is not connected to a powersource or ground). Power cord 60 is a direct current power cord having aplug end 61 which is a conventional plug to be received within aconventional cigarette lighter in automobiles. Plug 60 terminates at acoupling end 62 provided with male connectors 63, 64 disposed to engageand mate with female connectors 32, 33 of coupling 28. Plug 61 isadapted for a 12 volt DC battery and plug 51 is adapted for insertioninto a standard 120 volt AC outlet.

In a preferred use as a cushion or the like, it is desirable to provideenergy to the coils 24, 26 at a sufficient rate to enable as rapidheating as possible of the pad 10. In the preferred embodiment, directcurrent coil 26 is selected to have a resistive value of about 0.08 ohmsper foot and with a length of about 18 feet. Resistive coil 24 isselected to have a resistance of 11 ohms per foot and length of about 13foot. If faster heating is desired, higher resistive valves can be used.

As previously noted, both of resistive elements 24, 26 terminate atneutral connector 33 across a thermal switch 30. Thermal switches arewell known in the art and preferably, thermal switch 30 is selected tobe a normally closed switch which opens in response to a sensedtemperature of 150° F. (i.e., 10° above the phase change temperature ofthe preferred phase change material).

With the construction thus described, the heating coils 24, 26 can beindividually heated by coupling 28 being secured to either of plugs 50,60. With the use of either direct current or alternating current, theresistive element 22 heats in response to the electrical energy. Theheat of the resisting element heats the phase change material 20 suchthat the phase change material 20 will undergo a phase change. Whenheating is complete, the cords 50, 60 may be removed and the pad 10 willretain its energy for a substantial period of time of about two to threehours. As a result, the pad can be heated through either direct currentor alternating current. It may be heated in a user's home or in a user'scar or place of business. In addition to the foregoing, the vinylplastic 18 is a microwave transparent material as is cloth 12. Theparticular phase change material 20 thus described is microwavereceptive. Accordingly, the entire pad 10 may be placed in aconventional consumer microwave oven and the necessary energy to heatthe phase change material may be applied through microwave energy. Formicrowave applications, the user may open opening 16A by separatingfasteners 40, 41 and folding the coupling 28 into the interior of thecloth covering 12. This prevents the coupling 28 and its metallicelements from being directly exposed to the interior of a microwaveoven.

B. Alternative Embodiments

FIGS. 9 and 10 show alternative embodiments of the present invention. InFIG. 9, a pad 10′ is shown having a microwave transparent outer plasticenvelope 18′ which is sealed to define a sealed interior 20′. Twopackets 30′ of identical construction are contained within the interior20′.

Each packet contains a layer of open cell foam material 32′ and a liquid33′. The liquid (e.g., water) is impregnated within the foam 32′ and theliquid and foam 32′ are surrounded by a microwave transparent plasticpouch 34′ which completely surrounds the foam 32′ and liquid 33′ andwhich is sealed. In the forming process, the pouch 34′ may be partiallyevacuated to partially compress the foam 32′. Each pouch 30′ may be ofthe construction and method of manufacture such as that disclosed incommonly assigned U.S. Pat. No. 5,300,105.

Positioned between the pads 30′ is a heating coil shown schematically asa resistor 22′ accessible at an external electrical plug 28′. Asmentioned, ends 18 a′ and 18 b′ of envelope 18′ are sealed. In theschematic view of FIG. 9, end 18 b′ is shown open simply to illustratethat coil 22′ extends through sealed envelope 18′ to a plug 28′accessible on the exterior of envelope 18′.

As with the previous embodiment, the plug 28′ permits the coil 22′ to beheated electrically through either an AC or a DC source. The heating ofthe coil 22′ heats the packets 30′ which retain the heat after the plug28′ is disconnected from a source of electrical power. Alternatively,the pads 30′ may be heated through microwave energy. The pads 30′ maycontain a phase change material but need not. Instead, the pads 30′ maycontain a liquid 33′ as disclosed in the aforementioned U.S. Pat. Nos.5,300,105 or 5,339,541.

FIG. 10 shows a still further embodiment for a pad 10″ containing amicrowave transparent outer envelope 18″ sealed at ends 18 a″ and 18 b″and which includes internal dividing walls 20″ separating the interiorof outer envelope 18′ into three stacked and separately sealed volumes21″, 22″ and 23″. Layers 21″, 23″ may be filled with any suitable heatretention medium such as a phase change fluid 33″ as previouslydescribed or a heat packet such as packets 30′ of FIG. 9. A coil 122″ iscontained within chamber 22′ and accessible through an external plug 28″which may be plugged into a wall outlet or to a source of DC power.Accordingly, the design permits the heat retention mediums withinvolumes 21″, 23″ to be heated either electrically or through microwaveradiation.

With the foregoing specification, it has been shown how a thermalheating device has been attained in a preferred embodiment of a heatingpad. The device may be heated through either microwave energy,alternating current through a standard wall outlet or direct currentthrough an automobile cigarette lighter or the like. While the foregoingdescription has been made with reference to a preferred embodiment of aheating pad, it will be appreciated that a thermal heating deviceaccording to the present invention can be provided in a wide variety ofuses and applications such as clothing (footwear, mittens or the like),beverage or food containers or warmers or other devices which aredesired to be heated and retain heat for a substantial period of time.Accordingly, it is intended that the scope of the claims of the presentinvention not be limited by the preferred embodiment but shall includesuch modifications and equivalents as shall occur to one of ordinaryskill in the art having the benefit of the teachings of the presentinvention.

What is claimed is:
 1. A thermal heating and heat storage devicecomprising: (a) a warmer comprising: (i) a plastic member defining aninterior volume; (ii) a phase change material for storage of latent heatpositioned within the interior volume of said plastic member; (iii) anelectrically resistive heating element positioned in thermallyconductive contact with said phase change material; (A) said heatingelement being selectively controllable, upon direction of electriccurrent therethrough, to heat said phase change material to atemperature sufficient for storage of latent heat therein; (B) saidheating element being positioned within the interior volume of saidplastic member; (iv) a thermal switch arrangement constructed andarranged to control heating of said electrically resistive heatingelement; (v) an electric power cord having a first end with a coupling;said first end and coupling being positioned exterior to the interiorvolume of said plastic member; said coupling is adapted to be coupled toa selected one of sources of alternating and direct current; saidelectric power cord being in electrically conductive communication withsaid electrically resistive heating element; and (b) an outer coveringdefining an internal volume receiving and surrounding said warmer, saidcovering having at least one openable and closeable end; (i) saidcovering and said at least one openable and closeable end being sizedfor receipt therein of said warmer; (ii) said at least one openable andcloseable end constructed and arranged for selective closure of said atleast one openable and closeable end; and (iii) said covering isconfigured for storage of food, to be maintained warm, therein.
 2. Adevice according to claim 1 wherein: (a) said outer covering is cloth.3. A device according to claim 1 wherein: (a) said outer coveringincludes a hook-and-loop fastener.
 4. A device according to claim 3wherein: (a) said thermal switch arrangement is constructed and arrangedto prevent heating of said warmer to a temperature above 150° F.
 5. Adevice according to claim 4 wherein: (a) said thermal switch arrangementis constructed and arranged to control heating of said phase changematerial to a temperature no higher than 10° F. above a temperature atwhich said phase change material begins to convert from a solid to aliquid.
 6. A device according to claim 1 including: (a) open cell foampositioned within the interior volume of said plastic member, along withsaid phase change material.
 7. A device according to claim 1 wherein:(a) said plastic member is flexible.
 8. A device according to claim 1wherein: (a) said plastic member is vinyl.
 9. A thermal heating and heatstorage device comprising: (a) a warmer comprising: (i) a plastic memberdefining an interior volume; (ii) a hydrocarbon containing phase changematerial for storage of latent heat positioned within the interiorvolume of said plastic member; (iii) an electrically resistive heatingelement positioned in thermally conductive contact with said phasechange material; (A) said heating element being selectivelycontrollable, upon direction of electric current therethrough, to heatsaid hydrocarbon containing phase change material to a temperaturesufficient for storage of latent heat therein; (B) said heating elementbeing positioned within the interior volume of said plastic member; (iv)a thermal switch arrangement constructed and arranged to control heatingof said electrically resistive heating element; (v) an electric powercord having a first end with a coupling; said first end and couplingbeing positioned exterior to the interior volume of said plastic member;said electric power cord being an electrically conductive communicationwith said electrically resistive heating element; and (b) an outercovering defining an internal volume having at least one openable andcloseable end, said covering receiving and surrounding said warmer; (i)said covering and said at least one openable and closeable end beingsized for receipt therein of said warmer; (ii) said at least oneopenable and closeable end constructed and arranged for selectiveclosure of said at least one openable and closeable end; and (iii) saidcovering is configured for storage of food, to be maintained warm,therein.
 10. A thermal heating and heat storage device comprising: (a) awarmer comprising: (i) a plastic member defining an interior volume;(ii) a phase change material for storage of latent heat positionedwithin the interior volume of said plastic member, said phase changematerial provided with a phase change temperature of about 140° F.;(iii) an electrically resistive heating element positioned in thermallyconductive contact with said phase change material; (A) said heatingelement being selectively controllable, upon direction of electriccurrent therethrough, to heat said phase change material to atemperature sufficient for storage of latent heat therein; (B) saidheating element being positioned within the interior volume of saidplastic member; (iv) a thermal switch arrangement constructed andarranged to control heating of said electrically resistive heatingelement; (v) an electric power cord having a first end with a coupling;said first end and coupling being positioned exterior to the interiorvolume of said plastic member; is adapted to be coupled to a selectedone of sources of alternating and direct current; said electric powercord being in electrically conductive communication with saidelectrically resistive heating element; and (b) an outer coveringdefining an internal volume having at least one openable and closeableend, said covering receiving and surrounding said warmer; (i) saidcovering and said at least one openable and closeable end being sizedfor receipt therein of said warmer; (ii) said at least one openable andcloseable end constructed and arranged for selective closure of said atleast one openable and closeable end; and (iii) said covering isconfigured for storage of food, to be maintained warm, therein.